In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document to selectively dissipate the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas of the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet and heated to permanently affix the powder image to the copy sheet.
After each set of copy sheets is produced and collected at a finishing station, a stapler or stitcher is activated to attach the sheets of each set to one another. In this way, stapled sets of collated copy sheets are produced. Copy sheets may be printed as a landscape or portrait. In landscape printing, the page is printed so that when positioned for reading, the page is wider than it is long. In portrait printing, the page is printed so that when positioned for reading, the page is longer than it is wide. It is desirable that the stapling device used in the finishing station be capable of providing at least a portrait staple, i.e. a staple in the upper left hand corner of a set of copy sheets having a portrait orientation, a landscape staple, i.e. a staple in the lower left hand corner of a set of copy sheets having a landscape orientation, and a dual staple, i.e. a staple in the upper left hand corner and lower left hand corner of a set of copy sheets having a portrait orientation. In order to reliably control the position of the staple in the copy sheets, the location of the stapling device must be accurately determined before the staple is inserted.
Heretofore, various approaches have been devised for sensing the position of movable objects. The following disclosures may be relevant:
U.S. Pat. No. 5,097,453; Patentee: Kobayashi et al.; Issued: Mar. 17, 1992.
U.S. Pat. No. 4,713,665; Patentee: Phelan; Issued: Dec. 15, 1987.
U.S. Pat. No. 4,578,674; Patentee: Baker et al.; Issued: Mar. 25, 1986.
U.S. Pat. No. 4,506,354; Patentee: Hansen; Issued: Mar. 19, 1985.
U.S. Pat. No. 4,247,922; Patentee: Jackson et al.; Issued: Jan. 27, 1981.
U.S. Pat. No. 3,893,064; Patentee: Nishihara et al.; Issued: Jul. 1, 1975.
The relevant portions of the foregoing patents may be briefly summarized as follows:
U.S. Pat. No. 5,097,453 discloses an ultrasonic ground speedometer utilizing the Doppler effect to determine the speed of a moving object by transmitting an ultrasonic wave toward the ground over which the object moves, and receiving the reflected wave with a receiver. An arithmetic circuit is employed to determine the Doppler shift resulting from the relative motion between the moving object and the ground, and thereby the ground speed of the moving object. The frequency of the transmitted wave is varied so as to produce a constant reflected wave frequency to the receiver.
U.S. Pat. No. 4,713,665 teaches an ultrasonic ground speed and direction sensor having a vehicle mounted transmitter and receiver. A signal processor is used to superimpose an attenuated, phase-shifted transmit frequency on the output of the receiver to cancel out cross talk between the transmitter and receiver. The signal processor further includes a phase-locked loop circuit which generates an output voltage having amplitude and polarity corresponding to the speed and direction of the vehicle, respectively.
U.S. Pat. No. 4,578,674 discloses a method and apparatus for wireless cursor control. The apparatus comprises a control base and a wireless mouse. The mouse has an infrared detector to receive an infrared reference signal, from the control base, which in turn drives an ultrasonic transducer therein. The ultrasonic signal produced by the mouse transducer is received by a pair of ultrasonic detectors located on the control base. Knowing the separation distance of the ultrasonic detectors located on the control base, the initial position of the mouse can be approximated as a function of the time difference between an interruption of the infrared reference signal and the corresponding interruption of the ultrasonic signal received by the control base. Subsequently, relative motion of the mouse is determined by the magnitude of the Doppler effect change in frequency of the ultrasonic signals received by the ultrasonic detectors located on the control base.
U.S. Pat. No. 4,506,354 teaches a system suitable for detecting the position of an object over a flat rectangular area, for example, a CRT screen. A pair of ultrasonic transducers, spaced apart from one another, are individually pulsed at several frequencies and receiving means, one or both of the transducers, receive echoed pulses which are reflected by the object present on the surface. A discriminator elects desired echoes in accordance with a time delay, whereby the frequency, the magnitude of the signals, and the elected echoes are used to measure the distance of the object from the transducers and to determine its position.
U.S. Pat. No. 4,247,922 discloses a system for detecting the position of moving vehicles, for example, a lift truck. More specifically, the system is designed for use in a warehouse to verify that specific loads which are carried by the lift truck are deposited in the proper location. The vehicle transmits a first signal indicating that the load has been deposited. Subsequently, a central station transmits a beam which is detected by a receiver on the vehicle, causing the transmission of a second signal by the vehicle. The second signal is generated in response to the receipt of ultrasonic signals by transducers located on the left and right sides of the lift truck, whereby the frequency of the second signal is indicative of the direction that the lift truck is facing while depositing the load.
U.S. Pat. No. 3,893,064 describes a signal discriminating device comprising a band-pass filter for selectively passing signal- and noise-frequency components. Discrimination of signal from noise is accomplished based upon the existence of the two frequency components in such a manner that no signal is passed when both components are detected, while the signal-frequency component is passed when the noise-frequency component is not detected.
In accordance with the present invention, there is provided an apparatus for determining the distance between a movable body and a stationary reference location. The apparatus includes first transducer means, permanently affixed at the reference location, for emitting an ultrasonic energy wave in response to a first oscillating signal having a selected period, and second transducer means, affixed to the movable body, for generating a second oscillating signal, also having the selected period, in response to receipt of the ultrasonic energy wave produced by the first transducer means. The apparatus also includes synchronizing means, responsive to the first and second oscillating signals, for measuring an elapsed time of a partial ultrasonic energy wave period sent from the first transducer means and received by the second transducer means; means, responsive to the synchronizing means and a difference between the number of complete ultrasonic energy signal cycles sent by the first transducer means and received by the second transducer means, for determining the total elapsed time for propagation of the ultrasonic energy wave; and arithmetic means for determining the separation distance between the movable body and the reference location as a function of the total elapsed time.
In accordance with another aspect of the present invention, there is provided an apparatus for positioning a stapling device relative to a set of sheets. The apparatus includes means for moving the stapling device, in a linear direction substantially parallel to an edge of the set of sheets, to a selected stapling position, and ultrasonic means for sensing the linear position of the stapling device while being moved by the moving means.
In accordance with yet another aspect of the present invention, there is provided a method of monitoring the position of a sheet stapling device, with respect to a stationary reference position, in an apparatus having means for transporting the stapling device in a linear direction, substantially parallel to an edge of a set of sheets. The method comprises the steps of generating a first oscillating signal, said signal having a frequency in the ultrasonic range. Using a first transducer positioned at the stationary reference position to transmit an ultrasonic energy wave in response to the first oscillating signal. Receiving the ultrasonic energy wave with a second transducer, operatively associated with the stapling device, said second transducer producing a second oscillating signal in response to the ultrasonic energy wave. Finally, determining the position of the stapling device as a function of the time required for the ultrasonic energy wave to propagate from the first transducer to the second transducer.